Fuel cell systems are increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers such as vehicles as a replacement for internal combustion engines, for example. Such a system is disclosed in commonly-owned U.S. Pat. No. 7,459,167, hereby incorporated herein by reference in its entirety. Fuel cell systems may also be used as stationary electric power plants in buildings and residences, as portable power in video cameras, computers, and the like. Typically, the fuel cell systems generate electricity used to charge batteries or to provide power for an electric motor.
Fuel cells are electrochemical devices that directly combine a fuel such as hydrogen and an oxidant such as oxygen to produce electricity. The oxygen is typically supplied by an air stream. The hydrogen and oxygen combine to result in the formation of water. Other fuels can be used such as natural gas, methanol, gasoline, and coal-derived synthetic fuels, for example.
The basic process employed by a fuel cell system is efficient, substantially pollution-free, quiet, free from moving parts (other than an air compressor, cooling fans, pumps and actuators), and may be constructed to leave only heat and water as by-products. The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells, depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack, with the plurality of cells commonly arranged in electrical series. Since single fuel cells can be assembled into stacks of varying sizes, systems can be designed to produce a desired energy output level providing flexibility of design for different applications.
A typical fuel cell is known as the polymer electrolyte membrane (PEM) fuel cell, which combines the fuel the oxidant to produce electricity and water. In order to perform within a desired efficiency range, a sufficient humidification of the polymer electrolyte membranes of the fuel cell should be maintained. The sufficient humidification desirably extends the useful life of the polymer electrolyte membranes in the fuel cell, as well as maintains the desired efficiency of operation. Therefore, it is necessary to provide a means for maintaining the fuel cell membranes in the humidified condition. Maintaining the fuel cell membranes in the humidified condition helps avoid a shortened life of the membranes as well as to maintain the desired efficiency of operation. For example, lower water content of the membrane leads to a higher proton conduction resistance, thus resulting in a higher ohmic voltage loss. The humidification of the feed gases, in particular at the cathode inlet, is desirable in order to maintain sufficient water content in the membrane. Humidification in a fuel cell is discussed in commonly-owned U.S. Pat. No. 7,036,466 to Goebel et al.; commonly-owned U.S. patent application Ser. No. 10/912,298 to Sennoun et al.; and commonly-owned U.S. Pat. No. 7,572,531 to Forte, each of which is hereby incorporated herein by reference in its entirety.
To maintain a desired moisture level, an air humidifier is frequently used to humidify the air stream used in the fuel cell. The air humidifier normally consists of a round or box type air humidification module that is installed into a housing of the air humidifier. Examples of this type of air humidifier are shown and described in U.S. Pat. No. 7,156,379 to Tanihara et al., hereby incorporated herein by reference in its entirety, and U.S. Pat. No. 6,471,195 to Shamanuki et al., hereby incorporated herein by reference in its entirety.
As part of a fuel cell system, a water vapor transfer (WVT) device, also known as a membrane humidifier, may be used to humidify the air stream entering the fuel cell stack. The WVT device transfers water vapor from an exhaust stream from the fuel cell stack to a feed stream entering the fuel cell stack. This is generally accomplished by using a water vapor transfer membrane that allows only water vapor to pass therethrough. This membrane may be permanently attached to a diffusion media layer. The locations where the membrane is attached to the separator are desirably leak free. The membrane and diffusion media layer combination may be referred to as a separator, a separator plate, or a membrane humidifier assembly.
It is known to manufacture a water vapor transfer separator consisting of a plastic plate with flow channels either machined or molded into the plastic plate. The gas diffusion and membrane layers are attached to the plastic plate using pressure sensitive adhesive (PSA). However, the PSA is difficult and time consuming to apply. Additionally, where the PSA has not been applied correctly, repair of separator may be time consuming and costly, possibly requiring replacement rather than repair. Furthermore, use of a plastic plate increases the overall dimensions of the separator plate.
An exemplary membrane humidifier for a fuel cell system that does not involve a plastic plate is disclosed in commonly-owned U.S. Pat. Appl. Pub. No. 2009/0092863 to Skala, which is hereby incorporated herein by reference in its entirety. The Skala patent application describes a membrane humidifier assembly for a membrane humidifier having a top layer formed from a diffusion medium and a bottom layer formed from a diffusion medium. The diffusion medium is formed from a glass fiber impregnated with an uncured resin. The resin is cured (a process referred to as “calendaring”) with heat and pressure. The curing process controls the thickness of the diffusion medium. An array of substantially planar elongate ribbons is disposed between the top and bottom diffusion medium layers. Appropriate alignment of the ribbons between the diffusion medium layers is time consuming and difficult. Furthermore, when the ribbons are fixed to the diffusion medium layers, the ribbons may be pressed into the diffusion medium layers, thereby creating high resistance areas militating against the flow of fluids through the gas diffusion mediums. A membrane is adhered to at least one of the top and bottom diffusion medium layers.
It would be desirable to produce a membrane humidifier assembly for a membrane humidifier, wherein the dimensions of the assembly, the material costs of the membrane humidifier and the assembly, and the assembly time of the membrane humidifier are minimized.